1. Field of the Invention
This invention relates to the molding of footwear soles, and is concerned in particular with the molding of soles from multiple components having different hardnesses.
2. Background of the Invention
It is known to provide shoe soles comprising combinations of two or more components having different hardnesses. The compounds are strategically configured and arranged to achieve optimum characteristics including comfort and support for the wearer's foot.
U.S. Pat. No. 4,798,010 (Sugiyama) describes a midshoe sole for sport shoes which comprises both hard and soft elastic elements. The elements are produced separately with complimentary configurations enabling them to be assembled and bonded together with an adhesive.
U.S. Pat. No. 3,042,948 (Di Nunzio) and U.S. Pat. No. 5,077,915 (Gross) both teach shoe soles having two components with different durometers. In each of these references a cavity is cut in one component, and the other component is shaped to fit into the cavity. In Gross, the two components are secured together with an adhesive, whereas in Di Nunzio the two components can be joined by vulcanization.
A major drawback associated with these prior art methods is their labor intensive nature, each requiring a careful shaping and matching of interlocked components, the sizes of which must be adjusted to produce differently sized soles. Each sole size must be separately molded and then have a cavity cut therein. The dimensions of the cavity are different for each shoe size and thus the dimensions of the shaped interlocking component are also different for each sole size. During molding, care must be exercised to insure that mating components are properly matched. Otherwise, the resulting composites will be flawed by voids and/or distortions.